Can ends are typically produced in a multi-operation process. In a first operation, circular blanks are cut from a sheet of the metallic end stock, typically aluminum or steel sheet, and the blank is formed into the basic end configuration, or "shell". In a second operation, a curl is produced on the outer periphery of the shell. (It is known to combine the curling operation within the blanking and forming die, but such operations are atypical and present problems of their own, and are of no concern to the present invention.) After curling, the end may be considered finished for some applications, but typically is further re-formed to include an easy-opening device, such as a ring pull tab or stay-on-tab. The term "ends" will be used herein to refer to shells, finished ends with easy-opening devices, and intermediate products in different stages of manufacture in between. Ends are sometimes called "lids".
The ever-increasing need for can ends in the beverage field has led can end producers to increase their productivity. Originally, can ends were formed in compound die processes having, for example, 2 to 4 pockets per press. (Each pocket has an upper die assembly and a lower die assembly.) Productivity increases in such presses were typically limited to speed increases of the press. Such speed increases have, for all practical purposes, reached their limit, and further substantial productivity increases in the older, smaller presses is unlikely.
Material usage is a major factor affecting can end prices. As mentioned, most compound dies in the past were of the two pocket type. Two finished ends per press stroke were stamped from a ribbon slightly wider than the blank size of 2 discs at 30.degree. longitudinally. This manufacturing method provided approximately a 6% loss in the remaining web material, plus slitting charges incurred from reducing the wide mill width of about 60 inches to approximately 6 inches for press stock. Thus, instead of employing 60 inch coil slit ten times, with each strip creating 6% scrap plus slitting charges, a substantial dollar savings could be realized by processing the full width 60 inch mill-strip.
A new generation of multi-out gang press-die systems was developed. These presses are double action multi-slide presses capable of stamping 20 ends per stroke from a 60 inch coil width. These systems are relatively low-speed and massive, with integrated ejection troughs and conveyors.
The one aspect of this "wide out" concept which was not fully appreciated was the new responsibility placed on the sheet rolling mill to make perfect, flawless 60 inch wide end stock. In the past, the mill had been able to recover a good percentage of the coil by selective slitting and scrapping. When full width coil is required, such salvage is not feasible, so high percentages of coil stock must be scrapped, re-melted, re-cast and re-rolled.
Thus evolved a need for a new method of manufacture, one that is capable of running at least 1/2 mill width coils, has 11-out dies, and preferably has the inherent capacity to utilize any width combination up to the 1/2 coil width. This concept dictates that since coil width is reduced the speed must be increased to provide a suitable ratio of overhead to productivity.
In order to achieve this high-speed capability in a gang press, the entire, so-called "wide out" concept should be replaced. Double action presses are too massive for high speeds, the ejection method too irrational to achieve the control needed, and end handling too unpredictable to apply to a new high speed process.
While many of the older, smaller presses were of the relatively simple single action design, in which a single ram moves upwardly and downwardly against a complimentary die, the larger presses have been of the double action type, in which the ram has a pair of punch members which move upwardly and downwardly, with the inner die member moving within the outer die member and, for at least a portion of its travel, independently of the outer punch member. Such double action presses have, of course, added to problems of control of the system, due to their complexity. There is a need, therefore, for a single action can end press operable in the large press environment.
Another problem of greater proportions with the increased size of multiple station forming presses is the removal of ends from the die assemblies in the large production presses. Unlike smaller presses, in which each station (i.e., set of upper and lower die assemblies) could have its own independent receiving chute or other apparatus, there is insufficient room at the cut line level of the larger presses for individual lanes of exit chutes. Because of this, belts or other similar bulk removal means have been employed in these larger presses. Such means have proved to be substantially less reliable than the individual lanes available on smaller systems, increasing the chances of jamming of the ends during their removal from the die and thus necessitating shutdown of the press. There is also a need, therefore, for a can end forming system for high output presses which provides for control of the ends during their discharge from the die such that more precise control could be realized with tooling more serviceable toward high production.